Bumping gaia.json for 2 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/d15adbd5c5b1
Author: gasolin <gasolin@gmail.com>
Desc: Merge pull request #14526 from gasolin/issue-948283

Bug 948283 - [BB][refactor] host in single style folder, r=arnau

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https://hg.mozilla.org/integration/gaia-central/rev/59be55b90b5a
Author: gasolin <gasolin@gmail.com>
Desc: Bug 948283 - [BB][refactor] host in single style folder

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "4252fd24e16fabe52b9df6e32a94a54809c97c8c", 
+    "revision": "d15adbd5c5b14787893d40e4f7d13aca057b9df6", 
     "repo_path": "/integration/gaia-central"
 }